The present invention relates to a dc/dc converter and, in particular, to a method and apparatus for controlling the current transmitted to a load through a switching transistor comprising a part of the converter.
Switching transistors employed in dc/dc converters can be actuated in various ways, a transformer often being used if it is desired to keep the actuating power as low as possible. As an example, German Pat. No. 2,014,218 discloses a circuit for controlling the current through a switching transistor wherein current flow is initiated by a control transformer. In this prior art circuit, turn-on pulses of a first polarity are generated by a clock pulse generator, and the base current of the switching transistor is provided by positive feedback of the load current to the control circuit. The clock pulse generator terminates current through the switching transistor by means of a short pulse of opposite polarity. A disadvantage of this circuit is that the current flowing in the base circuit is too high for some applications. Moreover, it is difficult to control the circuit with external signals and parameters such as, for example, the voltage across the load resistance.
It is therefore an object of the present invention to provide a method and apparatus for actuating a switching transistor wherein the power loss is low and the current through the load is easily and quickly controlled by external control signals.